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Merrimack’s Cancer Drug Misses Mark in Mid-Stage Trial, Shares Tumble

Merrimack Pharmaceuticals has been keeping a close eye on an ongoing series of mid-stage clinical trials of its experimental cancer drug, hoping they will prove its worth to regulators and investors. It released the results from one of those studies today, and the numbers aren’t pretty.

Merrimack found that patients taking its drug in combination with the chemo agent paclitaxel fared no better than those dosed with paclitaxel alone. The hazard ratio for progression free survival was 1.0, meaning, in a statistical sense, that there was no difference between the two groups of patients. Worse, patients dosed with the Merrimack drug reported more side effects, like vomiting (31.4 percent for those on MM-121 and paclitaxel, compared to 18.8 percent for those on paclitaxel alone), diarrhea (73.6 percent versus 43.2 percent), and pulmonary embolisms (5 percent versus 1.2 percent), which are dangerous clots that get to the lungs.

Shares of Merrimack fell more than 15 percent in pre-market trading.

MM-121 is a cancer antibody targeting HER-3, or ErbB-3, a receptor on the surface of cancer cells. Merrimack licensed the drug to Sanofi in 2009, and has set up an ambitious program to test it. The 223-patient study that the company provided top-line results for today is part of a series of trials including roughly 1,000 patients testing MM-121 both as a first- and second-line treatment in ovarian, breast, and lung cancer.

For its part, Merrimack has said that it didn’t expect all of these studies to hit their goals. Rather, it has been hoping to find out not just if MM-121 works, but if diagnostic tests can accurately predict who should take it—and who shouldn’t—with the idea of designing a cheap, efficient late-stage trial to test the drug. So the company is saying now, for instance, that the drug was much more effective at stopping tumors from spreading in a subgroup of people with two specific biomarkers linked to ErbB-3, than it was in those without those biomarkers.

That being said, none of that is going to mean a thing to investors until at least one of these studies produces positive results. MM-121 similarly missed its mark in a small study of lung cancer patients earlier this year.

Ben Fidler is Xconomy's Deputy Biotechnology Editor. You can e-mail him at bfidler@xconomy.com Follow @benthefidler